This invention relates generally to improvements in power tools used in the installation of threaded fasteners, particularly specialized threaded fasteners of the type used in aerospace and related industries. More specifically, this invention relates an improved fastener installation tool of the type described in U.S. Pat. No. 5,553,519 having a power-driven socket for installing a threaded nut onto a threaded fastener, a fixture pin for normally retaining the threaded fastener against rotation during nut installation, and a clutch mechanism for permitting fixture pin rotation in response to a torque overload condition thereby preventing fixture pin breakage. The improved fastener installation tool incorporates an improved clutch unit adapted for quick and easy fixture pin disengagement, and displacement to an out-of-the-way position to permit quick and easy fixture pin removal and replacement.
A variety of specialized fasteners have been developed and are widely used in the aerospace and related industries, wherein these threaded fasteners have been designed to meet specific design criteria and uses. One example of a specialized aerospace fastener comprises a so-called “Eddie” bolt in the form of a threaded bolt adapted for power-driven installation of a threaded nut onto a threaded shank, without requiring access to the bolt head. That is, such fasteners are designed to fit through a preformed opening in a substrate or other structure with the bolt head inaccessibly disposed at a blind side thereof. The bolt shank protrudes through the substrate opening with a threaded shank end exposed for screw-on installation of a threaded nut. The shank end is formed to include a small shallow recess of typically hexagonal cross section for receiving a mating fixture pin designed to hold the bolt against rotation as the threaded nut is installed. Power-driven installation tools are known for use in installing such fasteners, including a small fixture pin disposed coaxially within a power-driven socket for installing the threaded nut while the fixture pin holds the bolt against rotation.
In a typical fastener application, using a power-driven installation tool of the type described above, the fixture pin engages and supports the fastener shank, and progressively retracts within the power-driven socket as the threaded nut is rotatably advanced onto the threaded bolt shank. At least some friction between the bolt and the substrate assists the fixture pin in retaining the bolt against rotation during nut installation. In recent years, however, particularly with the advent of composite material substrates in aircraft, friction contributes minimally to bolt retention during nut installation, and this is especially true when the substrate opening is coated or lined with a sealant material having a typical low coefficient of friction. Accordingly, on some occasions, the fixture pin is the only structure preventing bolt rotation during nut installation. Torque loads between the power-driven nut and the bolt can sometimes be transmitted directly to the fixture pin, resulting in over-torqueing and breakage of the fixture pin. When this occurs, it has been necessary to remove the installation tool from service for appropriate repair or replacement.
U.S. Pat. No. 5,553,519 discloses an improved fastener installation tool wherein the fixture pin is carried by a spring-loaded clutch to prevent a fixture pin torque overload condition. More particularly, the fixture pin is carried by a cam wheel having an externally toothed or lobed configuration defining detent seats engaged by a spring-loaded cam pin. During normal operation, the cam pin retains the cam wheel and fixture pin against rotation, thereby also retaining the bolt shank engaged with the fixture pin. However, in the event of a torque overload condition, the cam pin springably retracts to permit limited rotation of the cam wheel and fixture pin sufficient to protect the fixture pin against torque overload damage.
While this above-described fastener installation tool with spring-loaded clutch provides a significant advance in the art by effectively safeguarding the fixture pin against torque damage, the assembled components do not facilitate quick and easy access to the fixture pin. That is, portions of the clutch assembly must be disassembled in order to access the fixture pin as may be periodically required, for example, to interchange fixture pins of different sizes suitable for engaging and retaining bolts of different sizes.
Accordingly, there exists a need for further improvements in and to fastener installation tools of the type having a fixture pin carried by a torque overload clutch, wherein the fixture pin can be accessed quickly and easily and without any significant disassembly of tool components, to facilitate fixture pin removal and replacement. The present invention fulfills these needs and provides further related advantages.